1. Field of the Invention
This invention relates to a sheet conveying apparatus for a printer, facsimile or the like and an image reading apparatus thereof.
2. Description of Related Art
Conventionally, among an image reading apparatus such as a digital copier, a printer, or a facsimile, there is an original document processing apparatus, such as a sheet conveying apparatus, being openable-closable against an original document table for automatically feeding an original document (a sheet) to an image reading apparatus. The image reading apparatus serves to read an image of the original document by performing exposure upon the original document automatically fed from the original document processing apparatus.
Further, in respect of a discharge portion of the original document processing apparatus, there is one where the sheet is directly discharged after a reading process of an image, and the other is where an original document is switched back after an image of a front side of a double-sided original document is read, and is then further subject to reading of the backside, and is once again switched back and conveyed to be discharged.
A conventional original document processing apparatus having the foregoing structure is shown in FIG. 5. In the drawing, the discharge portion of the original document processing apparatus is structured with a pair of reverse-discharge rollers 201a, 201b for performing a switchback operation and for performing a discharging operation.
During the discharging operation of the original document processing apparatus, the original document is conveyed with a prescribed speed by the conveying portion 203, and then, an image is read at a reading position 204, and then, the original document is guided to a discharge portion 202 by a C-guide 207, and then, the original document is discharged to a discharge tray 205 by a pair of reverse-discharge rollers 201a, 201b. 
During the switchback operation of the original document processing apparatus, after the original document is conveyed with a prescribed speed by the conveying portion 203 in the same manner as the above, and after an image is read at a reading position 204, the original document is passed through a primary conveying path R1 and is guided to the discharge portion 202 by a flapper 209 and by the C-guide 207. Then, after a rear edge of the original document passes a reverse-discharge sensor, the pair of reverse-discharge rollers 201a, 201b starts reversal while nipping the original document, and with the work of the flapper 209, the original document is conveyed once again to the conveying portion 203 so as to pass a conveying path R2.
With such structure, when a path of the conveying portion 203 is shortened for size reducing the original document processing apparatus, an original document having a maximum conveyable length would become crossed over at the discharge portion 202 during the switchback conveyance process; accordingly there is an original document processing apparatus where the pair of reverse-discharge rollers 201a, 201b are separably structured.
With such structure, when reading the first surface, the pair of reverse-discharge rollers 201a, 201b are separated before starting the original document reading process. During this process, the reverse-discharge roller 201a serves as a driving roller and starts to drive in an original document discharge direction. After the reading of the first surface of the original document is completed (after the rear edge of the original document has passed the reading portion 204), the pair of reverse-discharge rollers 201a, 201b nips the original document, and then, after the rear edge of the original document passes the reverse-discharge sensor 208, the pair of reverse-discharge rollers 201a, 201b drives in reverse for conveying the original document to the conveying portion 203.
After the switchback where the original document is delivered to the conveying portion 203 by the discharge portion 202, the pair of reverse-discharge rollers 201a, 201b separates and momentarily ceases driving, and then, when the conveying portion 203 delivers the original document until the front edge of the original document reaches the reading position 204 for reading the second surface, the reverse-discharge roller 201a starts driving in the original document discharge direction in the same manner as the reading of the first surface.
After the reading of the second surface, the pair of reverse-discharge rollers 201a, 201b nips and conveys the original document and once again repeats reversal in means to sort the order of the discharged original document and finally completes the reading operation.
During the reading operation, when the original document processing apparatus conveys an original document having a maximum conveyable length, the pair of reverse-discharge rollers 201a, 201b is required to be separated since the front edge of the original document having been switchback conveyed again to the discharge portion 202 and the back edge of the original document being in the midst of switchback conveyance would cross over at the discharge portion 202.
Further, an electricity removal needle 206 is normally disposed near the pair of reverse-discharge rollers 201a, 201b, and serves to remove electric charge of the original document and prevent the matching trouble of the original document caused by electrification.
However, the conventional original document processing apparatus had the following problems during the discharge operation and the switchback operation.
When the path of the conveying portion 203 is shortened for size reduction of the apparatus where the original document processing apparatus conveys an original document having a maximum conveyable length, the front edge of the original document and the back edge of the original document would cross over at the discharge portion 202 during the switchback conveyance. Therefore, the pair of reverse-discharge rollers 201a, 201b are separably structured so that the pair of reverse-discharge rollers 201a, 201b would not affect the front edge of the original document and the back edge of the original document being conveyed in a different direction, respectively.
In such case, the electricity removal needle 206 arranged nearby the pair of reverse-discharge rollers 201a, 201b makes contact with the original document and serves to remove electricity, nevertheless, during a switchback conveyance of the original document having maximum length, one end portion would overlap with the other end portion causing the original document to be discharged without having the front edge of the original document to contact with the electricity removal needle 206 and result to a risk of stacking trouble caused by electrification, due to the fact that the front edge of the original document is released by a nipping portion of the pair of reverse-discharge rollers 201a, 201b and discharged while the rear edge of the original document being in the midst of switchback conveyance would still be left at the discharge portion 202.
It is an object of this invention to solve the foregoing problems by providing a sheet conveying apparatus capable of steadily removing electricity from a sheet even during a switchback conveyance and to provide an image reading apparatus thereof.